If you look at the wires coming from the motor, there is 5 wires. The black with red stripe, and red with black stripe are the two you need. Take a 12 volt source, and touch these two wires, if your motor is good, it should move. Reverse the wires to get the motor to go the other way.
I chased a strange servomotor issue last season. Gears had worn enough that they periodically would not mesh. CPU took this as too much cable resistance and would send sled into failure mode. Early on shutting off and restarting sled would cure the failure mode and sled would run fine. Got worse over time and restart would not clear issue. Cycling the servo by hand would clear it. Didn't want to drop $350 for unreturnable servo if that was not the issue. Troubleshot enough to determine this was the root cause. Bought new servo and no issues since.
My sled has 6500 miles on it and now the servo has decided to turn backwards and not open the valves up. The code was up at start up if I didn't cycle it by hand. I'm am thinking with this many miles it has given out because if wires were sliced somewhere the servo wouldn't work? What do you guys think, time for a new servo?